This invention relates to filter systems, and more particularly to a filter system for a diesel engine utilizing a rolling regeneration diesel particulate trap.
FIG. 1 illustrates a prior art filter system 10 for a diesel engine 12. An exhaust line 14 is provided between the diesel engine 12 and the filter system 10. The filter system may include a housing 16 that includes at least a first section 18 and a second section 20. The first section 18 typically includes a flow-through monolith 22 therein and wherein the flow-through monolith is coated with a catalyst such as platinum. The exhaust gas from the diesel engine 12 includes a variety of constituents including NO and particulate matter which typically is in the form of a carbon-based material. The catalyst on the flow-through monolith 22 promotes the reaction of the NO with oxygen also present in the exhaust gas to form NO2. However, the reaction is not efficient enough to completely convert all of the NO in the exhaust gas to NO2. Thus, as shown in FIG. 1, both NO and NO2 leave the first section 18 of the filter and enter the second section 20 of the filter system. The second section 20 typically includes a wall flow monolith 24 therein. Wall flow monoliths are known to those skilled in the art and typically are manufactured from a ceramic material in a manner to provide a plurality of through hole cells running the longitudinal length of the monolith. The cross-sectional area of these through hole cells is extremely small, on the order of 10 microns. Wall flow monoliths are capable of trapping 99+ percent of the particulate emissions from a diesel engine. However, wall flow monoliths can become plugged very easily due to the very small openings of the through hole cells. As shown in FIG. 1, NO2 in the exhaust gas can be used to oxidize the carbon to form NO and CO, thus removing some of the particulate blocking the wall flow monolith. However, the amount of NO2 present in the exhaust gas from the diesel engine or generated in the flow-through monolith 22 may not be sufficient to completely oxidize the particulate blocking the wall flow monolith. Accordingly, the engine must be operated in order to generate substantial amounts of NO2 necessary to oxidize all the carbon and other particulate matter blocking the wall flow monolith. Otherwise, the wall flow monolith must be cleaned in another fashion.
Thus, it would be desirable to provide a filter system for a diesel engine which resulted in the wall flow monolith being plugged less often and providing an alternative means for regenerating the trap. The present invention overcomes deficiencies in the prior art and provides alternatives and advantages thereto.
The invention includes a rolling regeneration diesel particulate filter and filtering process that reuses NO produced in the process to generate additional amounts of NO2. One embodiment of the invention includes a process including flowing diesel engine combustion exhaust through a filter system including a first and a second section. The first section is positioned upstream of the second section with respect to the flow direction of the exhaust. The first section includes a foam constructed and arranged to trap carbon-based particulates in the exhaust. A first catalyst is carried by the foam to promote the conversion of NO in the exhaust from the diesel engine to NO2. The NO2 is used to oxidize particulates trapped by the foam to form CO and NO. The first catalyst or a second catalyst on the foam further promotes the oxidation of CO to CO2, and the oxidation of NO, generated by the reaction of NO2 with carbon, to generate additional NO2. The second section of the filter system includes a wall flow filter having a plurality of through hole cells formed therein running the longitudinal length of the wall flow filter. The wall flow filter is constructed and arranged to trap particulates in the exhaust and to promote the reaction of NO2 and carbon to produce NO and CO.
In another embodiment of the invention, the foam may include a ceramic foam made from Al2O3.
In another embodiment of the invention, the ceramic foam may also include ZrO2.
In another embodiment of the invention, the first catalyst may include platinum. The platinum may be coated on the foam in a loading of at least 25 grams per cubic foot of foam.
In another embodiment of the invention, the foam may have a porosity ranging from 80% to 90% and higher.
In another embodiment of the invention, the foam may include 10 to 60 pores per inch.
In another embodiment of the invention, the wall flow filter may include 25 to 300 cells per square inch of cross-sectional area of the monolith.
In another embodiment of the invention, the filter system may include a housing. The first and second sections of the filter system may be carried in the housing.
Another embodiment of the invention includes a rolling regeneration diesel particulate filter trap having a first and a second section. The first section is positioned upstream of the second section with respect to the direction of exhaust flow through the trap. The first section includes a foam constructed and arranged to trap carbon particulates in the exhaust. A first catalyst is carried by the foam to promote the conversion of NO in the exhaust flowing through the trap to NO2. The NO2 is used to oxidize the carbon particulates trapped by the foam to form CO and NO. The first catalyst or a second catalyst in the foam further promotes the oxidation of the CO to CO2 and the oxidation of NO, generated by the reaction of NO2 and C to generate additional NO2. The second section of the trap includes a wall flow filter having a plurality of through hole cells formed therein running the longitudinal length of the filter. The filter is constructed and arranged to trap particulates in the exhaust and to promote the reaction of NO2 and C to produce NO and CO.
Another embodiment of the invention includes a diesel engine exhaust filter system including a catalyzed foam filter and wall flow filter combination, wherein at least a portion of the wall flow filter surrounds a portion of the catalyzed foam filter and so that exhaust may flow through the catalyzed foam filter and then flow through the wall flow filter.
Another embodiment of the invention includes a diesel engine exhaust filter system having a plurality of filter combinations, and wherein each filter combination includes a catalyzed foam filter and wall flow filter, and wherein at least a portion of each wall flow filter surrounds a portion of a catalyzed foam filter and so the exhaust may flow through the catalyzed foam filter and then flow through the wall flow filter.
These and other objects, features and advantages will become apparent from the following brief description of the drawings, detailed description of the preferred embodiments, and appended claims and drawings.